Changes in Equity (Rollforward) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Balances	$ 3,954,925	$ 3,921,241	$ 3,849,528	$ 3,775,989	$ 3,921,241	$ 3,775,989
Dividends declared	(52,591)	(52,585)	(52,751)	(53,504)
Noncontrolling investors of USS	(2,410)	(7,504)
Share repurchases		(106,529)	(93,136)	(84,308)
Equity-based compensation	8,633	9,429	8,016	6,695
Net income	78,765	190,836	196,746	204,827	269,601	401,573
Other comprehensive loss, net of tax	186	37	(52)	(171)	223	(223)
Balances	3,987,508	3,954,925	3,908,351	3,849,528	3,987,508	3,908,351
Common Stock
Balances	646	646	645	645	646	645
Balances	646	646	645	645	646	645
Treasury Stock
Balances	(1,624,808)	(1,525,113)	(1,261,837)	(1,184,243)	(1,525,113)	(1,184,243)
Share repurchases		(106,529)	(93,136)	(84,308)
Equity-based compensation	953	6,834	816	6,714
Balances	(1,623,855)	(1,624,808)	(1,354,157)	(1,261,837)	(1,623,855)	(1,354,157)
Additional Paid-In Capital
Balances	1,183,776	1,181,012	1,160,139	1,160,048	1,181,012	1,160,048
Equity-based compensation	7,838	2,764	7,366	91
Balances	1,191,614	1,183,776	1,167,505	1,160,139	1,191,614	1,167,505
Retained Earnings
Balances	4,553,882	4,419,296	4,109,034	3,958,320	4,419,296	3,958,320
Dividends declared	(52,591)	(52,585)	(52,751)	(53,504)
Equity-based compensation	(158)	(169)	(166)	(110)
Net income	75,496	187,340	194,302	204,328
Balances	4,576,629	4,553,882	4,250,419	4,109,034	4,576,629	4,250,419
Accumulated Other Comprehensive Loss
Balances	30	(7)	130	301	(7)	301
Other comprehensive loss, net of tax	186	37	(52)	(171)
Balances	216	30	78	130	216	78
Noncontrolling Interests
Balances	(158,601)	(154,593)	(158,583)	(159,082)	(154,593)	(159,082)
Noncontrolling investors of USS	(2,410)	(7,504)
Net income	3,269	3,496	2,444	499
Balances	(157,742)	(158,601)	(156,139)	(158,583)	(157,742)	(156,139)
Redeemable Noncontrolling Interest
Balances	151,014	143,614	139,930	111,240	143,614	111,240
Noncontrolling investors of USS				28,690
Noncontrolling investors of USS	1,400	7,400
Balances	$ 152,414	$ 151,014	$ 139,930	$ 139,930	$ 152,414	$ 139,930